The present invention relates to an apparatus and a method for monitoring heat efficiency of a heating furnace. The apparatus for monitoring heat efficiency of a heating furnace includes: an exhuast gas flow volume detection unit which dectects an exhaust gas flow volume discharged from a heating furnace; a CO & O2_ measurement unit which measures carbon monoxide (CO) and oxygen (O2_) in the heating furnace; a temperature detection unit which detects temperatures of the inside and the outside of the heating furnace; and a control unit which calculates heat efficiency of the heating furnace based on at least one unit of status information of the inside and the outside of the heating furnace, detected or measured by the exhuast gas flow volume detection unit, CO & O2_ measurement unit, and temperature detection unit, and outputs at least one from alarm and error information if the calculated heat efficiecny of the heating furnance is out of a predetermined heat efficiecy section. The present invention provdies the apparatus for monitoring heat efficiency of a heating furnace which can provide alarm and error inforamtion immediately if the calculated heat efficiecny of the heating furnance is out of a predetermined heat efficiecy section.